1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to decoding an audio signal, and more particularly, to decoding parametric-encoded audio signals.
2. Description of the Related Art
Most related art high quality audio encoding apparatuses use a time-frequency transform method. According to this method, coefficients obtained by transforming an input audio signal into frequency domain by using transformation methods, such as a modified discrete cosine transform (MDCT), are encoded. In this case, however, when a target bit rate is lowered, the expressed sound quality is also reduced.
A parametric encoding method has been conventionally used for encoding an audio signal at a low bit rate. Examples of the parametric encoding method include a harmonic and individual lines plus noise (HINL) method and a sinusoidal coding (SSC) method. In parametric encoding methods, an original audio signal is modeled using component signals having predetermined characteristics, then, the component signals are detected from the audio signal, and parameters indicating the characteristics of the detected component signals are encoded. For example, if an audio signal is formed of a plurality of sinusoidal waves, the sinusoidal waves are detected from the audio signal, and only the frequency, phase, and amplitude of each of the detected sinusoidal waves are encoded, thereby achieving encoding an audio signal at a low bit rate.
FIG. 1 is a simplified block diagram of a related art parametric encoding apparatus. The parametric encoding apparatus illustrated in FIG. 1 operates on the assumption that an audio signal is formed of transient signals, sinusoidal signals, and noise. If a pulse code modulation (PCM) signal of the audio signal is input, a transient signal analyzer 110 analyzes transient signals included in the PCM signal, generates transient signal parameters, and a quantization unit 120 quantizes and encodes the transient signal parameters.
A transient signal synthesizer 130 synthesizes transient signals from the transient signal parameters, and a signal obtained by subtracting the synthesized transient signals from the original PCM signal is input to a sinusoidal analyzer 140.
The sinusoidal analyzer 140 analyzes sinusoidal signals included in the input signal, generates sinusoidal parameters, and a quantization unit 150 quantizes and encodes the sinusoidal parameters.
A sinusoidal synthesizer 160 synthesizes sinusoidal signals from the sinusoidal parameters. Thereafter, a signal obtained by subtracting the sinusoidal signals synthesized in the sinusoidal synthesizer 160 from the signal input to the sinusoidal synthesizer 160 is input to a noise analyzer 170. The noise analyzer 170 generates noise parameters from the input signal input thereto, and a quantization unit 180 quantizes and encodes the noise parameters.
A multiplexer 190 multiplexes the data of the encoded parameters and outputs the result as a bitstream.
FIG. 2 is a simplified block diagram of a related art audio reproduction apparatus including a parametric decoding apparatus and an equalizer. The parametric decoding apparatus illustrated in FIG. 2 is designed to decode the bitstream output from the encoding apparatus of FIG. 2. Here, an equalizer of a related art parametric decoding apparatus will be mainly described.
The input bitstream is divided into decoders with respect to component signals output by a demultiplexer 210. A transient signal decoder 220 decodes the bitstream and restores the transient signals. Similarly to the transient signal decoder 220, a sinusoidal decoder 230 restores the sinusoidal signals and a noise decoder 240 restores noise. Such signals are input together into a signal converter 250. The signal converter 250 converts input signals of time domain into frequency domain signals by using a fast Fourier transform (FFT) and MDCT. A frequency analyzer 260 analyzes the signals in the frequency domain and determines amplitudes of the component signals in each frequency band. A user input/output unit 270 receives a user input through a user interface 290, adjusts the amplitudes of the component signals in each frequency band according to the user input, and displays the amplitudes of the component signals in each frequency band to a user through the user interface 290. A signal converter 280 converts the frequency domain adjusted component signals of the user input/output unit 270 back into signals in time domain and outputs the signals through a speaker.
As described above, in the related art audio reproduction apparatus, the decoded signals are added together for a signal conversion and the amplitudes of the component signals in each frequency band are analyzed. Thus, finally restored signals may be different from the original signals. In addition, due to the equalizer modules 250 through 290, a configuration of the audio reproduction apparatus is complex. Consequently, a user adjusts the amplitudes for each signal component according to the parametric encoded model, and various sounds effects according to a user's desire cannot be applied.